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@@ -102,6 +102,9 @@ Please note that `nqptp` must run in `root` mode to be able to access ports 319
 
 Since `nqptp` uses ports 319 and 320, it can not coexist with any other user of those ports, such as full PTP service daemons.
 
+## Firewall
+If your system runs a firewall, ensure that ports 319 and 320 are open for UDP traffic in both directions. These ports are associated with PTP service and may be referred to as "PTP" in firewall rules.
+
 ## Programming Notes
 A _timing peer list_ can be sent to `nqptp` over port 9000. The list consists of the letter `T` followed by a space-separated list of the IP numbers of the timing peers. The list replaces any existing timing peer list.